The battle for the future of the Open Web is taking place as a new document model merges into a platform for highly graphical, interactive and information rich applications. Open source communities vie with dominant vendors Adobe, Microsoft, Apple, Cisco, Nokia and Google to stake out their claims as open source innovations collide with standards consortia and proprietary alternatives.

On Tuesday, the European court of justice, Europe’s supreme court, lobbed a grenade into the cosy, quasi-monopolistic world of the giant American internet companies.

It did so by declaring invalid a decision made by the European commission in 2000 that US companies complying with its “safe harbour privacy principles” would be allowed to transfer personal data from the EU to the US.

This judgment may not strike you as a big deal. You may also think that it has nothing to do with you.

Wrong on both counts, but to see why, some background might be useful. The key thing to understand is that European and American views about the protection of personal data are radically different. We Europeans are very hot on it, whereas our American friends are – how shall I put it? – more relaxed.

Given that personal data constitutes the fuel on which internet companies such as Google and Facebook run, this meant that their exponential growth in the US market was greatly facilitated by that country’s tolerant data-protection laws. Once these companies embarked on global expansion, however, things got stickier. It was clear that the exploitation of personal data that is the core business of these outfits would be more difficult in Europe, especially given that their cloud-computing architectures involved constantly shuttling their users’ data between server farms in different parts of the world.

Since Europe is a big market and millions of its citizens wished to use Facebook et al, the European commission obligingly came up with the “safe harbour” idea, which allowed companies complying with its seven principles to process the personal data of European citizens. The circle having been thus neatly squared, Facebook and friends continued merrily on their progress towards world domination. But then in the summer of 2013, Edward Snowden broke cover and revealed what really goes on in the mysterious world of cloud computing.

At which point, an Austrian Facebook user, one Maximilian Schrems, realising that some or all of the data he had entrusted to Facebook was being transferred from its Irish subsidiary to servers in the United States, lodged a complaint with the Irish data protection commissioner. Schrems argued that, in the light of the Snowden revelations, the law and practice of the United States did not offer sufficient protection against surveillance of the data transferred to that country by the government.

The Irish data commissioner rejected the complaint on the grounds that the European commission’s safe harbour decision meant that the US ensured an adequate level of protection of Schrems’s personal data. Schrems disagreed, the case went to the Irish high court and thence to the European court of justice. On Tuesday, the court decided that the safe harbour agreement was invalid. At which point the balloon went up.

“This is,” writes Professor Lorna Woods, an expert on these matters, “a judgment with very far-reaching implications, not just for governments but for companies the business model of which is based on data flows. It reiterates the significance of data protection as a human right and underlines that protection must be at a high level.”

This is classic lawyerly understatement. My hunch is that if you were to visit the legal departments of many internet companies today you would find people changing their underpants at regular intervals. For the big names of the search and social media worlds this is a nightmare scenario.

For those of us who take a more detached view of their activities, however, it is an encouraging development. For one thing, it provides yet another confirmation of the sterling service that Snowden has rendered to civil society. His revelations have prompted a wide-ranging reassessment of where our dependence on networking technology has taken us and stimulated some long-overdue thinking about how we might reassert some measure of democratic control over that technology. Snowden has forced us into having conversations that we needed to have.

Although his revelations are primarily about government surveillance, they also indirectly highlight the symbiotic relationship between the US National Security Agency and Britain’s GCHQ on the one hand and the giant internet companies on the other. For, in the end, both the intelligence agencies and the tech companies are in the same business, namely surveillance.

And both groups, oddly enough, provide the same kind of justification for what they do: that their surveillance is both necessary (for national security in the case of governments, for economic viability in the case of the companies) and conducted within the law. We need to test both justifications and the great thing about the European court of justice judgment is that it starts us off on that conversation.